1. Field of the Invention
This invention relates to apparatus operable to fasten together overlying metal sheets or webs. It is particularly concerned with the type of apparatus which for this purpose employs a co-operating piercing-and-forming punch and die set, to partially sever and displace a localised region of the sheets out of the planes thereof, and a flattening punch which then operates to spread the displaced region and thus fastens the sheets together with a clenching action. The invention also relates to control systems for such apparatus.
2. Description of the Prior Art
Apparatus of the foregoing type is disclosed in U.S. Pat. Nos. 1,343,003 and 1,394,915, and such apparatus at present in use normally has separate reciprocable rams, respectively associated with the piercing-and-forming die and the flattening punch, operated by a direct mechanical drive from a rotating crankshaft/eccentric arrangement. As a result the apparatus is of heavy fixed construction, with the obvious disadvantages that this entails--particularly that the work has to be brought to the apparatus for fastening, which may be inconvenient or even impossible--and adjustment of the clenching action to suit different types and thicknesses of work presents problems.